Air/oil mist generator

ABSTRACT

An air/oil mist generator (1A) including an accumulation chamber (2) inside which a mist of oil particles in air accumulates, the accumulation chamber (2) being provided with at least a first mist outlet (4), the generator (1A) comprising a nebulizer (3, 3A) feeding into the said accumulation chamber (2), the nebulizer (3) being optimised to operate at a first pressure level and being fed by a first line (BA) of compressed air at the said first pressure level, the generator (1A) further including a further nebulizer (3A) which also feeds into the accumulation chamber (2) optimised to operate at a second pressure level which is higher than the first pressure level, the further nebulizer being fed by a second line (AL) of compressed air at the second pressure level; the first line (BA) being optionally associated with a non-return valve (807) which prevents a backflow coming from the accumulation chamber (2).

This application claims priority to Italian Patent Application No.102019000006072 filed on Apr. 18, 2019, which is incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to an air/oil mist generator.

In particular, it relates to a mist generator to be used in alubrication system.

BACKGROUND ART

In the field of lubrication, mist generators are known which apply theVenturi tube principle. One of these systems is currently marketed bythe applicant under the trade name NEBOL.

This comprises a Venturi tube into which pressurised air is fed axially.At the throat of the Venturi tube (minimum passage section) there is anozzle envisaged for drawing up oil. In practice, the oil is suctionedvia the nozzle by the vacuum which is created in the minimum passagesection, by Venturi effect.

Alternative mist generation systems are also commonly known, for examplethose in which the mixing takes place without the use of a Venturisystem, but through what is known as a vortex system, such as thatdescribed, for example, in patent U.S. Pat. No. 4,335,804.

The advantage of the vortex systems with respect to the Venturi systems,is that they are more flexible. Indeed, the vortex is active (andtherefore is self-supporting and generates mist) within a broader rangeof air pressure and flow levels.

In practice, the pressure used by the system to generate the mistoriginates from the difference between the supply pressure of thenebulizer (whether of the Venturi or vortex kind) and the pressureinside the chamber where the mist is stored.

For example, if the pressure of supply (of the line) is of 6 bar, andthe pressure of the chamber is 4 bar, the system of generation of mistopera with a pressure of 2 bar.

A vortex system allows operation within in a broader range of pressureand flow levels than a Venturi system.

In all cases, the nebulizer (be it of the Venturi or vortex kind) thatproduces the mist, feeds into an accumulation chamber, which isconnected, through an outlet, to one or more user devices.

One problem encountered with the known systems is the fact that thesesystems are calibrated to work within a pressure range which is close tothe normal line pressure, i.e. 6 bar. In practice, when a user devicerequires a certain flow of air, a vacuum is created in the accumulationchamber which allows the nebulizer to operate thanks to the pressuredelta generated in the section spanning the nebulizer by virtue of therequired flow.

When user devices require very low air flows, the pressure in theaccumulation chamber does not drop sufficiently to allow the nebulizerto operate efficiently. Indeed, the pressure delta in the sectionspanning the nebulizer is insufficient to produce sufficient mist forlubrication.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an air/oil mistgenerator, which is improved with respect to the commonly knowntechnique.

A further object of the invention is to provide a generator which isable to supply a user device with a flow of air/oil mist in which theparticles of oil are finely dispersed, in an extremely homogeneousmanner, in the flow of air, even if a very low flow of air is required.

BRIEF DESCRIPTION OF THE FIGURES

Further characteristics and advantages of the invention will becomeapparent in the description of a preferred but not exclusive embodimentof the device, illustrated—by way of a non-limiting example—in thedrawings annexed hereto, in which:

FIG. 1 is a section view of a nebulizer which is part of the generatoraccording to the present invention;

FIG. 2 is a simplified section taken along the line II-II in FIG. 1;

FIG. 3 is a simplified section of a detail of the generator;

FIG. 4 is an exploded view of the detail circled in FIG. 3;

FIG. 5 is an overall perspective view of a generator according to thepresent invention;

FIG. 6 is a schematic view of a lubrication system comprising thegenerator in FIG. 5;

FIG. 7 is a section view of a variant of the generator according to thepresent invention, which features, specifically two nebulizers, ahigh-pressure one and a low-pressure one;

FIG. 8 is a plan view of a detail of the high-pressure nebulizer in FIG.7;

FIG. 9 is a perspective view of the generator in FIG. 7; and

FIG. 10 is a schematic representation of a supply system for thegenerator in FIGS. 7 and 9.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the aforesaid figures, reference number 1 denotes anair/oil mist generator as a whole.

Reference must be made initially to FIG. 5, which shows a possibleconfiguration of the generator. This can comprise a first 30 and asecond plate 31, which, through tie-rods 32, sandwich in a sealed manner(through gaskets T) a hollow cylindrical element 35 (or an element witha different section), so as to form a accumulation chamber 2. In theaccumulation chamber 2 an air/oil mist forms and, contemporaneously,this can act as an oil tank.

Outside the accumulation chamber 2 a gauge 37 (FIG. 6) can be envisagedto show the level of the oil present in the chamber. The gauge can be ofthe column type, formed of a small transparent tube which shows thelevel present in the accumulation chamber 2. Advantageously, there canalso be an electronic level sensor (not shown envisaged), connected tothe door 33, which measures the level of the oil present in the chamber.The sensor can be suitably interfaced with a control unit which tops upthe level via the further door 36 (for example, equipped with a manualvalve) or via other access ways to the chamber not shown.

The door 36, equipped with a valve, for example a manual valve, can alsobe used to drain the accumulation chamber 2 completely.

The first plate 30 features a plurality of through-holes (possiblythreaded, for coupling with plugs or quick couplings 4A), which definevarious air/oil mist outlets 4. In practice, when an outlet 4 is open,it is in communication with the interior of the accumulation chamber 2and (see FIG. 6), through each of these, the air/oil mist is deliveredto a user device U1, U2, via a suitable pipeline T1, T2. Advantageously,the pipelines T1, T2, can be intercepted by suitably controlled solenoidvalves E1, E2, or by manual valves.

According to the invention, the generator comprises at least onenebulizer 3 feeding right into the said accumulation chamber 2.

In the case illustrated, the nebulizer 3 is a ‘medium/low pressure’nebulizer and is clearly visible in FIG. 1.

In the present wording, the term ‘medium/low pressure’ means that it isconfigured to work in an optimal manner with an air intake pressureranging from 4 and 8 bar, preferably between 5 and 6 bar.

As can be seen, the nebulizer 3 can comprise a first nozzle 7 suppliedwith pressurised air, for example via the annular recess 40 suppliedthrough the passage 41, directly connected to the outlet of a pressureregulator R.

The nozzle 7 can feature first channels 8 supplied by the pressurisedair coming from the regulator R.

The channels 8 are clearly visible in FIG. 2, and each one of these isequipped with an outlet 8A on a surface 70 of the first nozzle whichdefines, at least partially, a first chamber 9 axially symmetrical withrespect to an axis A.

Specifically, the outlet 8A can be envisaged on a ‘cylindrical’ sectionof the first nozzle 7, which joins with a convergent section which willbe discussed later.

The channels 8 are positioned so as to generate a rotation (see arrowsin FIG. 1) of the air fed into the first chamber 9 around the said axisA; preferably these channels feed out tangentially with respect to thesurface 70, which is circular in section at the outlets 8A;.

The channels 8 can have a constant section, as shown, or can convergetowards the outlet 8A.

As can be seen in FIG. 1, the surface 70 of the first nozzle features atleast one section converging towards an outlet hole 10 (of the saidnozzle).

Advantageously the area of the outlet hole 10 should be greater than theoverall area of the outlets 8A, to allow the generation of a ‘vacuum’inside the chamber 9, whose utility will be explained later on.

Advantageously, the ratio between the overall area of the outlets 8A andthe area of the outlet hole 10 can be less than 0.7, preferablycomprised between 0.3 and 0.5. This is to create a vacuum area in thechamber 9, which allows the second nozzle 6 to draw up the lubricant.

In the configuration illustrated, the nozzle can be produced as a singlepiece, and features a shoulder 41 which, for assembly, abuts with a stop42 on the first plate 30.

Downstream of the first nozzle 7, towards the accumulation chamber 2,there is a divergent channel 11 envisaged, into which the outlet hole 10of the first nozzle 7 feeds. Advantageously, the divergent channel canbe defined by a passage with a frusto-conical section, produced in thefirst plate 30.

Going back to FIG. 1, it is known that the divergent channel 11 can bedefined by a wall 120 (for example, of the first plate 30) which isspaced apart from the perimeter of the outlet hole 11 (measurement M1shown in the drawing), at least on one surface comprising the outletsection of the said hole 10.

It has been found that this distance M1 can improve the dimension of theparticles fed into the accumulation chamber 2, probably because of thedetachment of a turbulent flow which forms directly downstream of thehole 10, because of the immediate restoration of pressure.

The distance M1 notably affects the quality and dimension of theparticles and it has been found that the minimum distance is at leasthalf the diameter of outlet D1, preferably the minimum distance M1 is atleast equal to a diameter of outlet D1.

The optimal measurement of M1 is essentially comprised between one andhalf times the outlet diameter and 4.5 times the outlet diameter.

The divergent wall 120 then, together with the rotation generated by thechannels of the first nozzle 7 (and therefore by the air), optimizes thedimension of the particles of oil expelled.

Another characteristic which affects the dimension of the oil particlesis the roughness of the wall 120 of the divergent channel 11. Therougher this section is, the better the coalescence of the larger sizedparticles, which are effectively removed from the flow.

It is presumed, indeed, that, upon encountering the “crests” on thesurface, the micro particles further divide, becoming still smaller.Part of the larger particles, meanwhile, stop in the troughs in thesurface and are thus excluded from the flow.

The optimal roughness value for the wall of the divergent channel 11 ispreferably 1.2μm Ra or higher.

Preferably, the roughness is achieved through processing which creates aspiral on the surface which ideally rotates counter to the rotationdirection of the vortex of air and oil.

The first chamber 9 can be further defined by a flat surface of anintermediate element 44 which can be pressed against the nozzle 7 by asuitable threaded element 45, for example screwed onto the first plate30.

Obviously, there are various OR-ring are present between theintermediate element and the first plate 30, but also between the firstnozzle 7 and the latter, to keep the pressurised air confined within thedesired position. The seals are clearly visible in FIG. 1.

Advantageously, the channels 8 can be defined by the nozzle 7, and bythe flat surface on which this is resting.

It is known that, for the inflow of oil, the nebulizer 3 also features asecond nozzle 6 which feeds into the said first chamber 9.

For example, the second nozzle 6 is inserted axially into a hole in theintermediate element 44, with appropriate OR-rings, and features a tip(in which a delivery hole 6A is made) which projects slightly withrespect to the aforesaid flat surface (of the intermediate element)facing the chamber 9.

Advantageously, as can be noted in FIG. 1, the second nozzle 6 featuresa second delivery hole 6A which is coaxial with respect to the axis A.Furthermore, the second nozzle 6 is associated with a supply channel CAwhich can draw up the oil present inside the accumulation chamber 2. Forexample, the supply channel features s passages 500 connected to a smallsuction tube 51, which draws up the oil accumulated in proximity to thebottom of the accumulation chamber 2. The supply channel can feature avalve 50 for the fine adjustment of the flow rate of the oil reachingthe second nozzle 6; advantageously, the flow is represented visually onthe gauge 34.

It has been found that, to achieve optimal nebulizer performance, it ispreferable that the second nozzle 6 feeds out at the outlet 8A of thesaid channels 8, preferably at the centreline of this outlet 8A.

Furthermore, it is useful for the second nozzle to feed out axially withrespect to the nozzle 7.

According to one aspect of the invention, the outlet hole 10 of thefirst nozzle 7 faces a condenser 5 envisaged inside the accumulationchamber 2, the condenser being preferably located downstream of thedivergent channel 11.

The condenser can feature dimensions which ensure the impression Iobtained by the extension of the conical wall 120 is entirely containedwithin the condenser.

It should be mentioned that in the present wording, the term ‘condenser’5 is used to define the plate-like element 5 positioned in front of theoutlet of the nebulizer 3 (advantageously supported by screws and bolts46 secured to the first plate 30).

Even if the condenser 5 is cooled by the inflow of air which hits it,its function is not to “condense” (in the physical sense of the word)the particles of oil which hit it.

At the most, it acts as a shield which facilitates the coalescence ofsignificantly sized particles of oil, which hit the condenser 5 andwhich cannot—because of the significant weight thereof—be transported bythe air into the spaces around the said condenser, inside theaccumulation chamber 2.

Later on in the description, with particular reference to FIG. 7, otherpossible configurations of the nebulizer 3 will be illustrated which,however, can feature the same fundamental dimensions described earlier.And this also applies to the further nebulizer 3A which will bedescribed with reference to FIG. 7.

The operation of the invention is clear from the description above andis essentially as follows.

The accumulation chamber 2 is pre-filled with a certain amount of oil,so as to be able to supply the primer 51, which is long enough to reachthe bottom of the chamber.

When lubrication is required by a user device, the regulator R sendspressurised air to the nozzle 7 (for example through the recess 40 andthe supply 41).

The pressurised air flows through the nozzle channels 8. After reachingthe chamber 9, the pressurised air assumes a vortex movement around tothe axis A of the nebulizer 3, because of the conformation and thearrangement of the channels 8.

Inside the first nozzle 7, the rotating air is conveyed towards the hole10 through the convergent section 70 of the said nozzle, increasing thespeed thereof and decreasing the pressure thereof.

Also, because of the relationship between the overall area of theoutlets 8A and of the hole 10, a vacuum forms inside the chamber 9 whichsuctions up the oil through the second nozzle 6, and the suctioned oilmixes with the air rotating in a vortex in the chamber 9, becoming apowder.

As soon as the air mixed with the oil is expelled through the hole 10,the divergent section (spaced apart by M1) generates an abrupt recoveryof the pressure of the air with the creation of vortexes and,contemporaneously, on the wall 120 of the divergent section theparticles of heavier oil accumulate, which are therefore forced out fromthe flow of air/oil.

Only the lighter particles remain suspended in the air which flows pastthe divergent section, and these smalls particles spread within theaccumulation chamber 2.

Given that the condenser 5 faces the outlet of the nebulizer 3, theformer collects part of the heavy oil particles and condenses themthereupon, which then fall onto the bottom of the accumulation chamber2.

The structure described above creates, inside the accumulation chamber2, a mist of extremely fine, suspended oil particles, with a diameterapproximately less than 1μm, the said mist being conveyed by the airwhich flows through the outlet 4.

The position of the outlet 4, on the roof of the chamber, subjects theparticles of oil to further selection, and only those which areextremely small and light can be conveyed by the pressurised air comingout of the outlet 4.

The system described above manages to generate extremely small oilparticles, which form very fine a mist and which can be conveyed by thepressurised air delivered by the generator 1, therefore providingexcellent lubrication.

Obviously, the particles which condense on the divergent wall 120, onthe condenser 5, or which do not manage to reach the outlet 4 becausethey are too heavy, precipitate onto the bottom of the accumulationchamber 2, mixing with the oil already present therein.

Advantageously, the accumulation chamber 2 is associated with adifferential pressure regulator 12, which feeds the compressed air intothe chamber when the difference between the internal pressure in theaccumulation chamber 2 and the supply pressure exceeds a pre-setthreshold.

This happens in the event that the demand from the user devices forlubricated air is particularly high and exceeds that which can behandled directly by the nebulizer.

In this case the differential pressure regulator 12 (FIGS. 3 and 4)carries a surplus of pressurised air inside the accumulation chamber 2,therefore allowing user devices U1, U2 to be supplied.

In the example described, the differential pressure regulator 12 cancomprise a valve element 13 with load applied by a spring 14 towards anopening 15 in communication with the supply of pressurised air (i.e. theregulator R); the spring 14 and the part of the valve element 13 are,meanwhile, in communication with the accumulation chamber 2 with theresult that, when the pressure in the accumulation chamber 2 falls belowa threshold pre-set according to the load applied by spring to the valveelement 13 (set, for example, at 2 bar), the valve element 13 releasesthe opening 15, thereby allowing the flow of air from the pressurisedair supply towards the accumulation chamber 2.

To prevent the infeed of air into the chamber having a negative effecton the mist present therein, the outlet of the differential regulator 12inside the accumulation chamber 2 features a silencer 16, which ‘breaksup’ the air fed so as to prevent significant interference with the mistpresent in the chamber.

In the description above, a generator 1 is described which features asingle nebulizer 3, which preferably works at medium/low pressure (i.e.through the pressure of supply lines which are common in many industrialcomplexes, the said pressure being approximately 6 bar).

A system such as the one described above is suitable to supply machines(for example cutting machines) with medium-range tools, and thereforewhich also require medium lubrication air flow rates, i.e. in the rangeof 2-8 m³/hour.

In the event of jobs with tools requiring a lower mist flow rate forlubrication and cooling, it has been found that the system describedabove is scarcely suitable. Or better, it has been found that in theevent of low flow rates, i.e. those below 2 m³/hour, the capacity togenerate a fine-particle mist falls noticeably. This is because theback-pressure present in the accumulation chamber 2 is too high to keepthe vortex system of the nebulizer 3 working.

The generator 1A, shown in FIGS. 7 to 10, has been devised to moreeffectively supply systems which feature user devices with highlyvariable air flow rates, and to keep the concentration of particles ofoil as constant as possible also in low-rate flows.

In the said figures, the same numerical references are used as thoseused to denote parts with a similar function to those already described.

As can be noted specifically from an analysis of FIG. 7, this generatoris essentially similar to that described earlier and this also featuresa nebulizer 3 whose function is identical to that described.

For example, the dimensions of the nebulizer 3 which are functional tothe generation of the mist, are those described earlier.

Nevertheless, in this specific configuration, the said nebulizerfeatures a nozzle 7 which, apart from defining the chamber 9, alsosupplements or better defines the divergent channel 11.

As mentioned earlier, the characteristics of the chamber 9 and of thedivergent channel 11, for the nebulizer 3, are exactly the same as thosealready described and do not therefore need to be reported again.

The simplification introduced by the addition, within the same piece, ofboth the chamber 9 and the divergent channel 11 is obvious. Indeed, theprocessing of the plate 30 in this variant, which is necessary in orderto house the nebulizer 3, if compared with that described in FIG. 1, ismuch more simple since the said plate features merely a through-holewith a cylindrical section, which houses and supports (also by means ofthe shoulder 41 and the step 42) the new nozzle configuration.

Obviously, also in the case described in FIG. 1, i.e. in which a singlenebulizer 3 is present in the generator 1, it will be possible to usethe simplified version of the nozzle 7 (which comprises the divergentchannel 11) and of the plate 30 described herein.

Going back, now, to the description of the generator 1A, the moreobvious difference with respect to that described for thesingle-nebulizer version, is the presence of a further nebulizer 3Aconfigured to generate a mist starting from a higher pressure withrespect to the nebulizer 3.

For example, the further nebulizer 3A features the same conceptualfunctioning as the nebulizer 3 but is configured to work at higherpressure levels and with lower flows.

Therefore, an important difference from the nebulizer 3 lies in the areaof the hole 10A and in the overall area of the outlets 8A (of whichthere can be only one).

Namely the first nozzle 7 may have an outlet hole 10 with an area thatis greater from the area of a further outlet hole 10A of the furtherfirst nozzle 7A.

Moreover the first nozzle 7 may have first channels 8 fed by pressurizedair, the further first nozzle 7A may have a single further first channel(80) or in any case may have a smaller number of further first channels80 with respect to number of first channels 8 of the first nozzle 7, fedby pressurized air.

The further nebulizer 3 can be configured to work with a supply pressureof between the 2 and the 4 times, preferably approximately 3 times, theline pressure, which is normally around 6 bar.

In practice, the two nebulizers 3, 3A are geometrically similar, but thefurther nebulizer 3A (and specifically the nozzle 7′) featuresdimensions which have been optimised to work (generating mist) with alower air flow.

This is immediately clear upon analysis of FIG. 8, which shows theconformation of the nozzle 7A in the part defining the chamber 9. Inpractice, this is a top-down view of the single nozzle 7A.

This features a single channel 80 (or, in any case, a smaller number ofchannels 8 with respect to the nebulizer 3). Also, the passage sectionof the channel 80, and consequently the area of the outlet 8A, issmaller than the outlet 8A of the channels 8 of the nebulizer 3. Thiscan be seen clearly upon analysis of FIG. 7, where the outlet 8A of thechannel 80 of the further nebulizer 3A is almost invisible if comparedwith those of the first nebulizer.

The remaining dimensions of the further nebulizer 3A essentiallycorrespond (or are at least in scale) with those of the nebulizer 3 buthave been optimised to work at a higher pressure.

Specifically, again as per FIG. 7, it is known that the semi-angle α1 ofthe opening of the divergent section 11 of the nebulizer 3 cancorrespond to the angle α2 of the further nebulizer 3A. The angle α1and/or α2 can be between 10° and 35°, preferably 15°.

The height H1 of the divergent section 11 of the nebulizer 3, cancorrespond to the height H2 of the said section of the further nebulizer3A.

The height H1 and/or H2 is preferably 1.5 times the diameter of outletD1, D2. Preferably the height H1, H2 is essentially twice the diameterof outlet D1, and/or four times the diameter of outlet D2.

The values stated above are particularly important; indeed, thesespecific measurements and angles were obtained through a rather long andcomplex optimisation process, based on trial and error. The range andthe dimensions described above are those which enabled the device toperform best.

The supply of air to the further nebulizer 3A can be obtained through aline AL, on which there may be a pressure booster 800 present (seepossible supply diagram in FIG. 10), which pressurises a tank 801 ofhigh-pressure air. Instead of the pressure booster, it is obviouslypossible to use a high-pressure compressor.

The pressure booster can be supplied to a suitable air handling unit 803and there can be a pressure gauge 804 envisaged on the supply line.

The further nebulizer 3A (high-pressure) can feature an oil supplyprovided via the said primer 51 described earlier. Advantageously, theline CA for the supply of oil to the further nebulizer does not featuresany fine adjustment system.

To complete the description of the diagram in FIG. 10, note that thesupply line BA to the nebulizer 3 is exactly the same as that describedearlier, with the sole further feature being a (possible) non-returnvalve 807, positioned on the supply of air to the medium/low pressurenebulizer 3.

The generator 1A in FIGS. 7-10 essentially operates as follows.

Preliminarily, a pre-set amount of oil is fed in, which settles on thebottom of the accumulation chamber 2.

The nebulizer 3 is then supplied with a line pressure (for example 6bar) and the further nebulizer 3A with a higher pressure, for example 20bar.

If air is not required by other user devices U1 or U2, the pressureinside the accumulation chamber 2 stabilises at approximately 20 bar.The non-return valve 807 prevents the passage of air from theaccumulation chamber 2 to the supply line BA to the nebulizer 3.

When air is required by the user devices, the pressure inside theaccumulation chamber 2 lowers according to the air flow rate required.

For standard air flow rates (i.e., for example, when processing normalsized tools), the internal pressure of the tank lowers to the same levelas the line pressure (i.e. approximately 5-6 bar).

In this case, both the nebulizer 3 and the further nebulizer 3A areworking. Nevertheless the flow rate of the mist (and also the air)provided by the further nebulizer 3A is lower (or negligible) incomparison with the flow rate of the mist (and the air) provided by thenebulizer 3 which, in practice, works within their optimal range ofpressure/flow rates and therefore with the maximum efficiency in termsof mist generation.

In practice, the further nebulizer 3A (which is configured to work atmuch higher pressure levels and with low flow rates with respect to thenebulizer) works, in any case, at a line pressure (low), but thecontribution thereof to the amount of mist is limited, and much lessthan that of the nebulizer 3, which is optimised to work at normalpressure levels too.

The further nebulizer 3A is configured to generate a vortex with higherpressure level and with lower flow rates with respect to the pressurelevel and the flow rates needed to generate a vortex in the firstnebulizer.

In the event that an additional air flow rate is required by the userdevices, the pressure inside the chamber falls below a pre-set value.This is due to the fact that the air flow rate required exceeds themaximum air flow rate deliverable by the nebulizer 3 and by the furthernebulizer 3A, and therefore there is a decrease in the pressure in theaccumulation chamber 2.

In these conditions, the nebulizer 3 works at the maximum air flow ratethereof and the mist generated thereby is excessive with respect to thatwhich would be needed for simply the air flow rate passing through viathe nebulizers.

In these conditions, therefore the differential pressure regulator 12(present also in this configuration) intervenes, clearing an additionalpassage for air to be fed directly into the accumulation chamber 2,thereby increasing the air flow rate with respect to the oil mistgenerated present in the chamber, and therefore optimising the ratio ofthe oil/air fed out by the generator 1A; this prevents overly richlubrication, exactly as mentioned earlier in relation to the generator1.

In the event that the air flow rates required are, meanwhile, belowstandard, and this occurs, for example, when very small tools are used,the pressure in the accumulation chamber 2 rises above the optimaloperating zone of the nebulizer 3, which gradually produces increasinglyless mist. At the same time, as the pressure rises, the efficiency ofthe further nebulizer 3A increases, as the latter starts producing agradually increasing flow of mist, entering the optimal operating rangethereof.

When the pressure inside the accumulation chamber 2 exceeds a certainthreshold (for example 6.5), the non-return valve 807 (set, for example,to a pressure delta of 0.5 bar) intervenes, cutting off the nebulizer 3completely. The non-return valve also prevents the air leaving theaccumulation chamber 2 via the supply line to the nebulizer 3.

When the nebulizer 3 stops working, all the mist needed is generated bythe further nebulizer 3A, which operates within the optimal operatingrange thereof, i.e. at rather high pressure levels and very low flowrates.

The progressive decrease in the flow rate of the nebulizer 3, and theincreased efficiency of the further nebulizer 3A are an automaticconsequence of the increase in the pressure in the accumulation chamber2, due to the low air flow rate required.

The system illustrated, therefore, adapts automatically to the air flowrates required, maintaining an optimal amount of mist for lubrication atlow flow rates too.

It should be noted that the increase in the lubrication pressure doesnot only aid the generation of a very fine mist, but also enables themore efficient cooling of small tools, which receive both more air andmore oil, to the advantage of the said cutting process. A higherpressure of air also improves the removal of shavings produced by thesaid processing.

According to one variant of the generator 1A, a valve 805 may befeatured (for example an automatic valve, set according to the pressureof the accumulation chamber 2, or operated by a solenoid) which can cutoff the operation of the further nebulizer 3A, in particular operatingconditions.

This can be useful since the high-pressure air supplied to the furthernebulizer 3 is very costly to produce.

Therefore, for example, the valve 805 can be configured to automaticallyopen when the difference between the pressure inside the accumulationchamber 2 and the pressure of the supply to the nebulizer 3 (a linepressure of, for example, 6 bar) is near the minimum pressure needed tosupport a vortex in the nebulizer 3 (for example, 2 bar). This reductionin the pressure delta can, indeed, be a forewarning of either the needfor very low lubrication flow rates (and therefore the intervention ofthe further nebulizer is necessary) or an interruption in the need forair lubrication (and in this case no high-pressure air is wasted, withthe exception of that small amount needed to raise the pressure of theaccumulation chamber 2 to the maximum supply pressure).

Obviously, in a simplified embodiment, valves can be simply be envisaged(manual or automatic, controlled by a control unit) which activateeither the nebulizer 3, or the further nebulizer 3A or both, dependingon the processing to carry out.

Various embodiments of the innovation are described herein, but othersmay also be conceived using the same innovative concept

For example, the accumulation chamber 2 may have any conformation, andmay also be embodied as a pressurised tank configured differently fromthat described above, with any cross-section.

Furthermore, a separate (and suitably pressurised) oil tank from theaccumulation chamber 2, may be envisaged, for example, with acirculation system which carries the oil that accumulates in theaccumulation chamber 2 into the main tank.

The configuration of the nozzle 7 is optimal in terms of the embodimentthereof since the channel or channels 8, 80 are formed between thenozzle 7 and the flat surface of the intermediate element 44.Nevertheless, the channel or channels inside the nozzle may also beproduced by means of through-holes.

Furthermore, the nozzle 7 described herein is produced as a single part,which defines the chamber 9 equipped with a convergent section 70.Obviously, in variants of the embodiments, the nozzle 7 may be produceas multiple parts which are mutually assembled through gaskets.

1. Air/oil mist generator, comprising an accumulation chamber insidewhich a mist of oil particles in air accumulates, the accumulationchamber being provided with at least a first mist outlet, the generatorcomprising a nebulizer leading to said accumulation chamber, thenebulizer comprising a first nozzle fed by pressurized air, thenebulizer being fed by a first line of compressed air at a firstpressure, the generator further comprising a further nebulizer whichalso flows into the accumulation chamber, the further nebulizercomprising a further first nozzle fed by pressurized air, the furthernebulizer being fed by a second line of compressed air at a secondpressure that is higher than the first pressure, the first line beingoptionally associated with a non-return valve which prevents acounter-flow from the accumulation chamber.
 2. Air/oil mist generatoraccording to claim 1, wherein the further nebulizer is optimized and/orconfigured to generate a mist using a higher pressure with respect topressure needed to generate a mist by the nebulizer.
 3. Air/oil mistgenerator according to claim 1, wherein the further nebulizer isoptimized and/or configured to work with a lower flow rate with respectto the nebulizer.
 4. Air/oil mist generator according to claim 1,wherein the first nozzle has an outlet hole with an area that is greaterfrom the area of a further outlet hole of the further first nozzle. 5.Air/oil mist generator according to claim 1, wherein the first nozzlehas first channels fed by pressurized air, the further first nozzlehaving a single further first channel or having a smaller number offurther first channels with respect to number of first channels of thefirst nozzle, fed by pressurized air.
 6. Air/oil mist generatoraccording to claim 1, wherein the further nebulizer is fed through avalve configured to automatically open when the difference between thepressure inside the accumulation chamber and the pressure of the firstline is near the minimum pressure needed to support the operation of thenebulizer and/or wherein the non-return valve is set to cut off thenebulizer when the pressure inside the accumulation chamber exceeds apredefined threshold.
 7. Generator according to claim 1, wherein thenebulizer and/or the further nebulizer comprises a first nozzle fed bypressurized air, which has at least a first channel fed by thepressurized air, each channel being provided with an outlet on a surfaceof the first nozzle which at least partially defines a first chamberthat is axially symmetrical with respect to an axis, the channels beingoriented so as to generate a rotation of the air introduced into thefirst chamber around said axis, the surface of the first nozzleproviding at least one section converging towards an outlet hole, thenebulizer also providing a second nozzle fed by oil, so that the oil issucked through the second nozzle due to the flow of air passing throughthe first chamber.
 8. Generator according to claim 7, wherein the outlethole of the first nozzle flows into a divergent channel.
 9. Generatoraccording to claim 8, wherein the divergent channel is defined by a wallwhich is spaced apart with respect to the perimeter of the outlet hole,at least on a plane containing the exit section of the hole. 10.Generator according to claim 1, wherein the outlet hole of the nebulizerand/or of a further nebulizer faces a condenser provided inside theaccumulation chamber.
 11. Generator according to claim 1, wherein thesecond nozzle outlet faces the outlet of said channels, preferably athalf-way of the outlet.
 12. Generator according to claim 2, wherein thesecond nozzle has a supply channel which sucks the oil present in liquidform inside the accumulation chamber, the supply channel comprising aflow regulator.
 13. Generator according to claim 1, wherein theaccumulation chamber is associated with a differential pressureregulator, configured to introduce into chamber the compressed air, whenthe difference between the internal pressure of the accumulation chamberand the nebulizer supply pressure exceeds a predefined threshold value.14. Generator according to claim 13, wherein the differential pressureregulator comprises a valve element loaded by a spring in the directionof an opening in communication with the supply of pressurized air, thespring and part of the valve element being in communication with theaccumulation chamber so that, when the pressure in the accumulationchamber falls below a threshold value defined by the load of the springon the valve element, the valve element frees the opening allowing aflow of air from the supply of pressurized air to the accumulationchamber and/or in which the output of the differential regulator insidethe storage chamber includes a silencer.
 15. Lubrication system,comprising a generator according to claim 14.